Sound absorbing material



May 2l, 1935. J. MAzER y SOUND ABSORBING MATERIAL Filed July 25,

lNVENTOR ployed in the walls and 6 studios, etc., for definitely absorbing and Patented May 21., 1935 UNITI-:D STATES PATENT' omer.V

2,001,916y SOUND ABSOBBING MATERIAL Jacob Mazer, Stonehurst,1a. Applicationjuly 23, 1929, Serial No. 380k328 s claims.

My invention relates to sound-absorbing material and a method of making the same, and more particularly to materials such as are emceilings of auditoriums,

controlling reverberation of sound waves.

Various plans have' heretofore been adopted for controlling and absorbing sound waves, such as porous masonry materials, iibrous bodies, rigid cellular panels, etc.

These various materials have been open to objections such as the necessity of forming them at the place of installation, and in conjunction-with the walls or ceilings to be covered, as in the case of plastic or masonry materials; the fragile na.- ture of the fibrous bodies which are readily subject to damage through handling and which are subject to natural limitations by reason of the elasticity, size, etc., of various vegetable fibers, hair, etc., and the difficulty of applying preformed cellular units to spaces of various areas and contours.

One object of my invention is to providey soundabsorbing material which is highly elastic and flexible, so that it will yield under slight impacts such as those or" sound waves, and which can be handled Without damage and readily compressed K or expanded to snugly fill designated wall spaces. Another object of my invention is to provide a porous sound-absorbing body or unit having intercommunicating pores of desired sizes and wherein the walls of the pores are elastic.

Still another object of my invention is to pro-v vide a sound-absorbing unit whose exposed surface may be given a decorative or protective facing.

A further object of my invention is to provide a sound-absorbing body that is of generally improvedv characteristics in the way not only of sound-absorption, but which is simple of manufacture and conveniently handled and installed.

In the accompanying drawing, Figure 1 represents a face view of a portion of a sound-absorbing unit constructed according to my invention; Fig. 2 is a sectional view thereof; Fig. 3 shows a modification of the structure of Fig. 2; Fig. 4 shows still another modification thereof; Fig. 5 is a view, on a greatly enlarged scale, showing more clearly the cellular structure of the units, and Figs. 6 and '7 are face and edge views, respectively, showing a further modicatii.

MaterialI which I employ is of a sponge-like nature containing throughout the mass cells of desired sizes, depending upon the prevailing pitches o! sounds to be absorbed at a given loca- (Cl. 15d-4A) tion. Thus, for sounds of comparatively low pitch, such as those in the neighborhood ofthe first octave of the musical scale (64 vibrations per second), cells. of a given size will be effective in the absorption of those sounds, while in the neighborhood of the higheroctaves of the musical scale, the fifth, sixth and seventh.(1024, 2048 and 4096 vibrations per second, respectively), for example, cells of smaller size will be employed.

One composition of which my sound units may be formed consists of .an ordinary rubber compound containing sullcient sulphur to. effect vulcanizaton thereof in the usual manner. With this compound, I incorporate materials which may form cells in the rubber either by dissolving away portions of the rubber or by forming gases therein which will expand under heat and about which the rubber will become set upon vulcanization of the mass.

As one example of pore-forming ingredients,

I may employ vegetable matter which contains moisture or which will form gases upon the application of heat below temperatures at which vulcanization' is effected. For instance, wet sawdust or charcoal particles may be incorporated with the rubber. The-size of the cells will be determined by the size of the gas-forming or steam-forming particles. For example, sawdust and vegetable matter which is passed through a 20mesh screen will form larger cells than those., particles of sufficient lineness to pass through a mesh screen. In those cases wherein a generally inclusive sound-absorbing quality is desired, without special consideration of either the low pitch sounds or the high pitch sounds, I will monium carbonate, soda, etc., these substances forming gases when heated to comparatively low temperatures. When the mixture ,containing the gas-forming particles has been brought to a temperature at which the gases are produced, it is vulcanized, thus resulting in-a unit of sponge texture having the sound-absorbing and general physical characteristics aboveset forth, and may have the appearance of the structure shown in Figs. 1 and 2. Hydrocarbon substances, such as paraffin may also be employed.

Instead of producing a body having only-cells of a given size, or having cells of large andsmall be placed on a wall or ceiling with the smaller cells outermost, so that the sounds of higher pitch will be more readily absorbed by the body, while the sounds of lower pitch will be absorbed more completely within the portion 6 of the unit than would be possible by a unit containing only the small cells. f, g

Again. the unit may have a smooth facing I of rubber, paint, or other plastic material. In the case of a rubber facing, this facing could be either glued to the cellular body or vulcanized thereto. Again, .if the'body is vulcanized in a close-tting mold,y there will be a tendency for a skin to be formed on the surface of the article where the rubber contacts with the mold sides, thus producing a smooth exterior.

Another mixture which may be employed instead of rubber may consist of glue,Y glycerine, and glucose, as a base, and containing gas-generating material such as soda or son'le .of the other materials above-enumerated. 'Ihis mixture may contain from 50 to '70 pounds of softened glue, 20 to 30 pounds of 'glycerine, and 15 to 25 pounds of glucose, fthe amount of gas-generating material. being of coursev dependent upon the extent of porosity desired in the completed The body is preparedby mixing l thev glue, glycerine and glucose at temperatures preferably not much in excess of 100 centigrade and then adding the soda. lThe mixture is stirred until la. foamy condition occurs, and may then be placed in molds and permitted to cool. When cooled it will be of a permanently elastic spongelike nature.

A .body having the cellular end elastic eheracteristics of those above-described will, of course, absorb a considerable quantity of sound waves by reason .of its porous or cellular structure and by reason of its elasticity and the ilexibility of the mass as a whole, as well as of the walls of the cells, the sound waves being transformed into heat energy through the heating of the mass and the friction within the pores..

Other materials, such as felt which is made up v y of the fibers or hairs found in nature,r or on aniare very definitely limited because of theV -limitations of the raw material, as to size, length,

absorbing power, strength, durability, etc. 'I'hese have porosity, but the amount of porosity can be controlled only through a very limited extent; lt iseasily changedthrough handling and'pressure, and does not have the yielding quality of the material which I produce. Another very distinct feature and quality is thatv my material whileihighly porous, is a homogeneous mass of one piece, and not merely loosely associated ilbers or small particles.

In Figs. 6 and '1, I show/a structurecomposed of crossed strands III and Il which may extend along substantially straight lines in various directions, or .may be heterogeneously assembled.

These strands l0 and Il may be formed of rubber, in which case they can be vulcanized t0- gether at their points of intersection to form a homogeneous mass'. The vulcanization could be effected in a mold, with the application of heat, in a manner common in the rubber industry.

The strands can also be formed of other material such as asbestos, in case a re proof body is desired and one which is not subject to decay. Theasbestos or other strands of thread-like or ribbon-lilieform may be glued or cemented together to maintain them in unitary relation. The fibers of Figsdand '7 are preferably manufactured in such forni end of such materials asto possess predeterminedrphysical characteristics and they may be of sucliL diameter and spaced Such distances apart as will-produce a body having pores of a desired size andy number.

-The material may be made up in the form of units` or slabsy of convenient size which ymay be applied to Walls, ceilings, or the like, by gluing,

'nailing or the like, and its nexibiuty permits lt to be closely and accurately applied to curved surfaces, corners, etc., by unskilled workmen, with the assurance that the sound-absorbing capacity of the material when applied will be definitely known in advance, according tothe structure oi' the units. Again, the material is compressible and 'if a piece is slightly too large for a given piece, it can be compressed therein. Again, it may be stretched somewhat in order to fill a larger space.

when a unit ls stretched, te' e desired extent',

it can be either glued or fastened in such posi'- tion or, in the case of the porous rubber, it can be stretched by the workmen and held in such position until the heat generated by the stretching action has been dissipated, whereupon the unit will become set in an expanded position.

Also, the units being elastic can be placed in slightly-compressed abutting relation with one another, thus substantially eliminating marked visible lines of division which are usually present between sound-absorbing units of a more rigid nature.

Ordinarily, the elastic bodies will be largely cellular, that is, they will be composed almost entirely of cells divided' only by thin-walls, instead of being largely solid and containing cells spaced considerable distances apart.

I claim as my invention:-

1. A sound-absorbing body containing cells whose walls are flexible and highly elastic, and

of such thinness that they will vibrate under the influence of sound waves, the cells in one portion JACOB 

